1. Field of the Invention
The present invention relates to an integrated tunable resonance circuit. The invention relates furthermore to a voltage-controlled oscillator and to an integrated circuit.
2. Description of the Background Art
The invention falls within the field of integrated circuits (IC). It falls particularly within the field of integrated tunable resonance circuits for providing a high-frequency output signal with a (target) frequency dependent on a control signal. Resonance circuits of this type are used in many cases in high-frequency circuit arrangements (radio frequency, RF), such as voltage-controlled oscillators, amplifiers, tuners, etc., in transmitting/receiving devices of telecommunication systems.
U.S. Pat. No. 6,778,022 B1 discloses an LC parallel resonance circuit (FIG. 2A), whose oscillation frequency is set (tuned) by changing accordingly the value of variable capacitances of the parallel resonance circuit. For this purpose, capacitors are connected individually into the resonance circuit with the use of digitally controlled switching elements, which are connected in series to each capacitor, or are not connected to said circuit (FIG. 3).
It is a disadvantage here that the switching elements in the closed state represent a not negligible series resistance, which has a negative impact on the quality of the resonance circuit. If the quality of the width of the switching elements is increased, the stray capacitance of the switching elements increases, however. As a result, in the opened state, the total capacity of the resonance circuit increases, so that the maximum settable frequency and thereby the width of the tuning range in which the frequency can be set decrease. An increase in quality can therefore only be achieved at the expense of tunability or an improvement in tunability can be achieved only at the expense of the quality of the resonance circuit.